The present invention relates to a fuel injector system, and more particularly to a method of determining the end of motion of a fuel injector spool control valve.
Fuel injectors typically use a high pressure fluid acting on a relatively large area intensifier piston to compress fuel under a smaller area plunger. When fuel pressure is raised above a valve opening pressure, a needle check valve lifts to open the nozzle outlet, and fuel sprays into the combustion space within an engine.
To accurately control the timing of each injection event, the fuel injectors commonly include a solenoid actuated spool valve that opens and closes the fuel injector to the high pressure actuation fluid. The spool valve is essentially an armature movable relative to a solenoid coil located at each axial end of the spool valve.
Each injection event is initiated by energizing one coil to move the control valve to an open position, and each injection event is ended by actuating a second solenoid coil opposite the first coil to move the spool valve back to its closed position. The fluid-actuated fuel injector de-couples the injection quantity and timing from the operation of the engine to provide flexibility of main pilot fuel quantity, timing, and duration.
As the spool valve moves toward the actuated coil, the magnetic field within the unpowered coil varies, thereby producing an opposing voltage or back emf voltage signal in the unpowered coil. Typically, the back emf voltage signal is examined to determine when the spool has reached its full open or closed position. Control of the injection event through actuation of the coils is thereby effected through a feedback control loop.
Although effective, distinguishing when the spool valve has reached the end of travel through examination of the back emf may be difficult and relatively imprecise due to the extremely small timing envelope of an injection event. Moreover, end of travel determinations is further complicated due to dragging of the spool valve, otherwise known as “stiction” which may alter the back emf signal.
Accordingly, it is desirable to provide a method of reliably determining when a fuel injector spool control valve reaches the end of motion.